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THE AMERICAN NATURALIST [Vol. XL VIII 



We are therefore to look upon the variety as a delicately- 

 organized chemical compound. The various factors of 

 climate and soil may be compared to different physical 

 influences to which the original compound may be sub- 

 jected. As the chemist would expect reactions varying in 

 accordance with the physical stimuli used, so will the plant 

 react in agreement with the different environmental com- 

 binations. The extent to which this will change the nature 

 and appearance of plants is often far reaching. Cook, 

 working with cotton, has found that certain cultural condi- 

 tions at an early stage of growth will make profound dif- 

 ferences in the method of branching which determines the 

 whole subsequent development of the plant and affects 

 materially its economic value. Cultural and climatic reac- 

 tions often lead to error among those who assume them to 

 be mutative changes induced by the new conditions. That 

 these reactions may bring to light sub-races with heredi- 

 tary tendencies not hitherto called into expression and 

 which, by selection, may be secured as pure races, is the 

 probable explanation of many cases of supposed direct 

 climatic adaptation. 



Thus, realizing the true nature of a variety, we can 

 draw further upon the analogy of the chemist who investi- 

 gates an unknown substance by testing its reactions with 

 a large number of known reagents. In like manner the 

 breeder can only understand the true nature of the hered- 

 itary vital forces within a plant after he has tested and 

 calibrated its reactions against a variety of soil and cli- 

 matic factors. These reactions are of interest to the 

 farmer only in so far as they affect the economic value of 

 the variety as grown in his own locality but to the breeder 

 and student of heredity their importance is fundamental. 

 This is so because they enable him to classify, coordinate 

 and interpret the experimental results that he obtains. 

 This ability finally must form the basis of all rational pro- 

 cedure, whether one be engaged in the study of pure gen- 

 etics or in the operations of practical plant improvement. 



